(1) Field of the Invention
This invention relates to a valve comprising a valve housing including a partition defining an opening, and a tubular valve closure member slidably mounted in the opening and having an open end, a closed end and a peripheral wall defining a plurality of pores, the valve closure member being slidable to control pressure of liquid flowing from a space upstream of the partition to a space downstream thereof through the pores and to shut the opening with the closed end.
(2) Description of the Prior Art
The valve of the prior art has the disadvantage that, in normal use for controlling liquid pressure as the liquid passes through the pores defined in the peripheral wall of the valve closure member, foreign matter in the liquid gradually accumulates around the pores thereby clogging them. A well known method of removing such foreign matter clogging the pores is to apply a reverse flush, that is to wash the foreign out of the pores by causing a reverse flow of the liquid therethrough. Generally this reverse flush is effected by reversing the liquid flow in the main pipeline in which the valve is installed thereby to washing the clogging out of the pores. The matters thus suspended in the liquid is then carried downstream. However, this method has a possibility of raising downstream pressure at the time of reverse flushing.
Another known method is to take the valve closure member out of the valve housing so that the clogged pores can be washed. However this known method has certain disadvantages, such as, the necessity of stopping flow in the main pipeline, and the time and trouble necessary to disassemble and assemble the valve.
A further method is to provide a strainer upstream of the valve closure member in order to filter out foreign matter present in the liquid before they reach the valve, the strainer being removable from the valve housing for cleaning. This method again has the disadvantage of requiring an additional element, the strainer, and the trouble of removing it from and mounting it into the valve housing.